1. Field of the Invention
The present invention relates to a fuel vapor processing apparatus for temporarily storing a fuel vapor evaporated from a fuel tank of an internal combustion engine to discharge the stored fuel vapor to an intake pipe as appropriate in order to prevent the fuel vapor from being emitted to the atmosphere.
2. Description of the Related Art
The processing apparatus of the type mentioned above is generally referred to as a xe2x80x9ccanisterxe2x80x9d. FIG. 1 illustrates an example of a conventional canister. The illustrated canister 51 comprises a box-shaped casing 52 which is partitioned into a main chamber 54 and a sub-chamber 55 by a partition wall 53. The main chamber 54 and the sub-chamber 55 communicate with each other at their adjacent ends to form a generally U-shaped flow passage. In addition, the main chamber 54 and the sub-chamber 55 are filled with adsorbent material 56 made of activated charcoal or the like. A blocking valve 58 is attached to an air introducing port 57 formed on the other end side of the sub-chamber 55. The blocking valve 58 is open to the atmosphere through a filter 59. The blocking valve 58 is closed when the canister 51 is checked for a fuel vapor leaking therefrom. On the other hand, a fuel vapor introducing port 60 and a fuel vapor discharge port 61 are arranged in parallel on the other end side of the main chamber 54. The fuel vapor introducing port 60 communicates with a fuel tank (not shown), while the fuel vapor discharge port 61 is connected to an intake pipe, not shown, through a discharge pipe provided with a purge control valve in the middle (both of which are not shown).
In the canister 51 constructed as described above, a fuel vapor evaporated from the fuel tank is introduced into the casing 52 through the fuel vapor introducing port 60, and is adsorbed and held by the adsorbent material 56 as it flows from the main chamber 54 to the sub-chamber 55. In this way, the fuel vapor passes along the U-shaped flow passage comprised of the sub-chamber 54 and the main chamber 55 to ensure a large length of flow path, as compared with the cross-sectional area of the casing 52, so that the desorption performance (the ability of adsorbing and desorbing the fuel vapor) is efficiently provided. The fuel vapor adsorbed on the adsorbent material 56 is desorbed from the adsorbent material 56 and emitted to an intake pipe through the fuel vapor discharge port 61 and the discharge pipe by desorbing air introduced from the air introducing port 57 to the accompaniment of a negative pressure in the intake pipe introduced into the casing 52 through the fuel vapor discharge port 61, as the purge control valve is opened during a predetermined operating condition of the internal combustion engine. Also, when the desorbing air flows into the casing 52, dust included therein is captured by the filter 59 to prevent a failure of the blocking valve 58 and an increase in air flow resistance within the casing 52 due to the intrusion of the dust.
However, since the conventional canister 51 described above has the filter 59 for filtering the desorbing air, which is provided separate from and external to the canister 51, the canister 51 requires a larger space for the entire size which is increased by the separate filter 59. In addition, the conventional canister 51 has difficulties in the layout of the filter 59 since the canister 51 and the filter 59 must be laid out separately. While a canister integrated with a filter is also known, the filter is attached to the top or a side surface of a casing of the canister, thereby resulting likewise in an increased size of the canister.
The present invention has been made to solve the problem as mentioned above, and its object is to provide a fuel vapor processing apparatus which presents a high desorption performance and can be constructed in compact, including a filter, to improve the flexibility in layout.
To achieve the above object, the present invention provides a fuel vapor processing apparatus which is arranged between a fuel tank and an intake pipe of an internal combustion engine for temporarily storing a fuel vapor evaporated from the fuel tank to discharge to the intake pipe as required. The fuel vapor processing apparatus includes a casing formed with a fuel vapor introducing port communicating with the fuel tank, and a fuel vapor discharge port communicating with the intake pipe; a partition arranged in the casing for defining a filter chamber inside thereof which communicates with an air introducing port for introducing desorbing air from the atmosphere, wherein the partition partitions the casing into a first chamber (main chamber) and a second chamber (sub-chamber) with a spacing interposed therebetween, and the first and second chambers communicate with each other, and also communicate with the filter chamber, the fuel vapor introducing port, and the fuel vapor discharge port; a filter contained in the filter chamber for filtering the desorbing air introduced from the air introducing port; and an adsorbent material filled in the first and second chambers for adsorbing the fuel vapor introduced from the fuel vapor introducing port.
In this fuel vapor processing apparatus, a fuel vapor evaporated from the fuel tank flows into, for example, the first chamber through the fuel vapor introducing port formed through the casing. The inflow fuel vapor is adsorbed and held by the adsorbent material as it is flowing from the first chamber to the second chamber. The adsorbed fuel vapor is desorbed from the adsorbent material and emitted to the intake pipe through the fuel vapor discharge port by the desorbing air introduced through the air introducing port to the accompaniment with a negative pressure in the intake pipe which is introduced into the first chamber through the fuel vapor discharge port during a predetermined operating condition of the engine. Also, the filtering action of the filter on the desorbing air prevents an increase in air flow resistance in the first and second chambers due to intrusion of dust.
As described above, in the processing apparatus of the present invention, the interior space in the casing is partitioned by the partition into the main chamber and the sub-chamber which are filled with the adsorbent material, and communicate with each other. The main chamber is separated from the sub-chamber by a spacing corresponding to the width of the partition. Thus, the surface area surrounding the main chamber and the sub-chamber is increased to facilitate heating of the adsorbent material such as activated charcoal, which is cooled during desorption, with external heat, resulting in the advantage of providing a better desorption performance and accordingly a higher desorption performance. Also, since the internal space of the partition for partitioning the main chamber and the sub-chamber is utilized as the filter chamber for containing the filter, the processing apparatus can be constructed in compact to improve the flexibility in layout.
Preferably, in this case, the fuel vapor processing apparatus further comprises a blocking valve contained in the filter chamber downstream of the filter, wherein the blocking valve is closed when the casing is checked for a fuel vapor leaking therefrom.
According to this structure, the filtering action of the filter prevents a failure of the blocking valve due to intrusion of dust. Also, since the blocking valve as well as the filter are contained in the filter chamber, the processing apparatus can be constructed further in compact to further improve the flexibility in layout.